High efficiency centrifugal fan

ABSTRACT

A centrifugal fan has a blower wheel ( 12 ) with an annular array of vanes ( 15 ) mounted for rotation about an axis of rotation. Each vane has a concave leading surface with an inboard portion located more proximally to the axis of rotation having a smaller radius of curvature than an outboard portion located more distally from the axis of rotation.

TECHNICAL FIELD

[0001] This invention relates to centrifugal fans and blowers, and particularly to the configuration of their blower wheel vanes.

BACKGROUND OF THE INVENTION

[0002] Centrifugal fans are used in many applications for creating forced air streams. Air purifiers and humidifiers are among such applications. These fans typically comprise a blower wheel that is rotated by an electric motor. The blower wheel is mounted in a housing that has a port through which ambient air may be drawing axially inside the blower wheel, then radially through the blower wheel and finally out of the fan housing through a scroll.

[0003] The blower wheel itself comprises an annular array of spaced apart fan blades or vanes. The vanes are typically flat and oriented at a skewed angle to the blower axis of rotation. Some vanes however have been curved along a circular arc in an attempt to improve blower efficiency. This efficiency is the amount of electric energy as in watts needed to produce a quantity of air flow as in cubic feet per minute or CFM. Curved blower wheel vanes has been found to enhance efficiency to some degree in some applications. However, centrifugal fans are still lacking in efficiency in comparison to other type fans.

[0004] Accordingly, it is seen that a need remains for a centrifugal fan that is highly efficient. It is to the provision of such that the present invention is primarily directed.

SUMMARY OF THE INVENTION

[0005] In a preferred form of the invention a centrifugal fan has an annular array of vanes mounted for rotation about an axis of rotation with each vane having a concave leading surface with an inboard portion located proximally to the axis of rotation having a smaller radius of curvature than an outboard portion located more distally to the axis of rotation.

[0006] In another preferred form of the invention a centrifugal fan has a blower wheel for drawing air axially into the wheel and then radially through the wheel and with the blower wheel having an array of vanes with leading surfaces oriented at an angle of attack to air inside the wheel that varies between vane inboard and outboard edges at a non uniform rate.

BRIEF DESCRIPTION OF THE DRAWING

[0007]FIG. 1 is a perspective view of a centrifugal fan that embodies principals of the invention in its preferred form.

[0008]FIG. 2 is an enlarged view of a portion of the blower wheel of the fan.

[0009]FIG. 3 is a cross sectional view of one of the vanes of the blower wheel.

DETAILED DESCRIPTION

[0010] With reference next in more detail to the drawing there is shown a centrifugal fan having a blower wheel 12 mounted for rotation within a housing 13 with a scroll 14. It is driven by an unshown electric motor in a clockwise direction as viewed in FIGS. 1 and 2. The blower wheel has an annular array of spaced apart fan blades or vanes 15. The fan is of conventional construction and operation save for the shape of the vanes 15. As the blower wheel rotates it draws air in through the housing intake 17, radially through the wheel and then out of the housing through the scroll 14.

[0011] The blower wheel vanes are better shown in FIGS. 2 and 3. The vanes are all identical here and are seen to have a concave surface as their leading surface and a convex surface as their trailing surface. Each blade has an inboard end or edge 20 that is proximal to the wheel axis of rotation and an outboard end or edge 21 that is distal the axis. Of prime importance here is the fact that the concave leading surface is not simply a circular arc but rather of a more complex shape. It is seen to have a smaller radius of curvature nearer its nearer edge 20 than it does proximal its outboard edge 21.

[0012] In the preferred embodiment shown that portion of this surface that extends from the outboard edge 21 is along a circular arc of a radius R1 of 459 mils. A little beyond half way to the proximal edge 20 its merges with and changes to a sharper curve of a radius R2 that here is 125 mils. From here the concave leading surface merges with a final portion of a radius R3 that here is 336 mils. Thus the relative ratio of their radii of curvatures is approximately 3 to 4.

[0013] Fans with blower wheel vanes of this shape have been found to yield a 30% improvement in blower efficiency over those that have a concave leading surface of uniform curvature. This is believed to be attributable to the accompanying angle of attack to air inside the wheel being acute adjacent to the inboard edge and obtuse adjacent to the outboard edge. In other words, the high inboard angle of attack is more efficient in causing the air stream entering the housing to make the right angle (omnidirectionally) turn into the blower wheel vanes. Once that turn has been effected then the more gentle angle nearer the outboard edge of the vanes facilitates flow vis-a-vis power consumption. Whether or not this is the case has not been proven. However the improvement in efficiency has been proven. Of course, other degrees and lengths of curvature may be had and do yield improvement in efficiency. The ones just identified with specificity have so far been found to be the best.

[0014] It thus is seen that a centrifugal fan is now provided with substantially improved efficiency. Although it has been shown and described in its preferred form, it should be understood that the specific contour of the leading surface of the blower wheel vanes is only that preferred at this time and that other contours and curvatures may be had that also provide improved fan efficiency without departure from the spirit and scope of the invention. 

1. A centrifugal fan having an annular array of vanes mounted for rotation about an axis of rotation and with each vane having a concave leading surface with an inboard portion located more proximally said axis of rotation having a smaller radius of curvature than an outboard portion located more distally said axis of rotation.
 2. The centrifugal fan of claim 1 wherein said inboard and outboard surface portions have relative radii of curvature of approximately 3 to
 4. 3. A centrifugal fan having a blower wheel for drawing air axially into the wheel and then radially through the wheel and with the blower wheel having an array of vanes with leading surfaces oriented at an angle of attack to air inside the wheel that varies between their inboard edges proximal to the wheel axis of rotation and their outboard edges distal to the wheel axis of rotation at a non uniform rate.
 4. The centrifugal fan of claim 3 wherein said vane leading surfaces vary from an acute angle of attack adjacent their inboard edges to an obtuse angle of attack adjacent their outboard edges. 